How to heat treat ht200, HT300 heat treatment process

HT200 heat treatment method].

1. Stress annealing (or artificial aging).

Eliminates residual stresses that exist inside the casting after casting. Stress-relieving annealing is often required: (residual stresses can cause warping and cracking of castings).

Generally 500-550. The higher the heating temperature, the faster the stress is relieved. The higher the temperature, graphitization and pearlitization will occur, reducing performance. The holding time is generally 5

min/mm

Compute. Later.

min speed with the furnace cooling to 150-200 out of the furnace, air cooling.

In order to eliminate or reduce the internal stress of the casting, natural aging or artificial aging can be carried out for castings without other heat treatment

Natural aging: more than 6-12 months at room temperature. For example, the aging of large beds is generally used in this way. But the production efficiency is low. The relief of internal stresses is also limited. Generally, artificial aging (stress relief annealing) is used.

2. Gray cast iron softening annealing and normalizing process: the surface of the casting forms a thin layer of white mouth layer due to rapid cooling, which is difficult to process, and the commonly used heat treatment process is: softening annealing is usually used 900-950.

The annealing and holding time is 2-3h. Then the furnace is cold. During the slow furnace cooling process, A decomposes into F+ graphite and becomes P+ graphite.

Therefore, the structure after normalizing is p+ graphite.

3. Quenching and tempering of gray cast iron: Quenching and tempering are rarely used for gray cast iron. Isothermal quenching is commonly used instead of quenching and tempering, and isothermal quenching obtains higher mechanical properties.

The structure of cast iron is distributed on the substrate for graphite, and heat treatment can not change the shape of graphite, and the strength can only be improved by heat treatment to strengthen the matrix. In fact, quenching and tempering are often used to improve wear resistance and fatigue limits.

HT200] is the grade of gray cast iron, HT stands for gray cast iron, HT is the abbreviation of gray cast iron in Chinese pinyin, and gray cast iron HT200 refers to the gray cast iron with a minimum tensile strength of 200MPa. Material Name: Gray Iron 200; Standard: GB T

9439-2010；Material hardness: 163 255HB.

HT200 Cast Iron! Annealing before machining (manual aging if hardness is required).

It can remove internal stress, reduce hardness (especially the surface), and facilitate processing.

Artificial aging can be: furnace temperature 200, heating speed 100, insulation temperature: 500 550, insulation time: 4 6 hours, cooling speed: 30, furnace temperature: 200.

HT200 heat treatment has three situations and corresponding methods:

1. Stress relief annealing (or artificial aging): eliminate the residual stress existing inside the casting after casting. Stress-relieving annealing is often required

Residual stress may cause warping and cracking of castings) is generally 500-550. The higher the heating temperature, the faster the stress is relieved. The higher the temperature, graphitization and pearlitization will occur, reducing performance.

The holding time is generally calculated as 5min mm. After 30-50, min speed with the furnace cooling to 150-200 out of the oven, air cooling. In order to eliminate or reduce the internal stress of the casting, natural aging or artificial aging can be carried out for castings without other heat treatment

Natural aging: more than 6-12 months at room temperature. For example, the aging of large beds is generally used in this way. But the production efficiency is low. The elimination of internal stress in the cleaning base is also limited. Generally, artificial aging (stress relief annealing) is used.

2. Gray cast iron softening annealing and normalizing process: the surface of the casting forms a thin layer of white mouth layer due to rapid cooling, which is difficult to process, and the commonly used heat treatment process is: softening annealing is usually used 900-950.

The annealing and holding time is 2-3h. Then the furnace is cold. During the slow furnace cooling process, A decomposes into F+ graphite and becomes P+ graphite.

Therefore, the structure after normalizing is p+ graphite.

3. Quenching and tempering of gray cast iron: Quenching and tempering are rarely used for gray cast iron. Isothermal quenching is commonly used instead of quenching and fire, and isothermal quenching obtains higher mechanical properties.

The structure of cast iron is graphite distributed on the matrix, and heat treatment can not change the shape of the graphite, and the strength can only be improved by heat treatment to strengthen the matrix. In fact, quenching and tempering are often used to improve wear resistance and fatigue limits.

HT300 Heat Treatment Process Specification:

Large parts are prone to residual stresses after machining, and all these internal stresses must be eliminated. The usual heating temperature for stress relief annealing is 500 550 and the holding time is 2 8 h, and then air cooling (ductile iron). With this process, 90-95% of the internal stress of the casting can be eliminated, but the structure of the cast iron does not change.

If the temperature exceeds 550 degrees or the holding time is too long, it will cause graphitization, which will reduce the strength and hardness of the casting.

Normalizing of ductile iron: The purpose of normalizing of ductile iron is to obtain the pearlite matrix structure, and refine the grains and uniform structure to improve the mechanical properties of the casting. Sometimes normalizing is also the preparation of ductile iron surface quenching on the tissue, normalizing is divided into high-temperature normalizing and low-temperature normalizing.

The high-temperature normalizing temperature is generally not more than 950 980, and the low-temperature normalizing is generally heated to the co-folding temperature range of 820 860. After normalizing, it is generally necessary to carry out tempering treatment to eliminate the internal stress generated during normalization.

Quenching and tempering of ductile iron: In order to improve the mechanical properties of ductile iron, the casting is generally heated to more than 30 50 (AFC1 represents the final temperature of formation A when heating), and then quenched into oil after heat preservation to obtain martensitic structure. In order to properly reduce the residual stress after quenching, tempering should be carried out after quenching, and the low-temperature tempering structure is tempered Mahalobis as a residual bainite and then spheroidal graphite.

This kind of tissue has good wear resistance and is used for parts that require high wear resistance and high strength. The medium temperature tempering temperature is 350-500 After tempering, the structure is tempered with quenchite and spherical graphite, which is suitable for thick parts that require good wear resistance, certain effective stability and elasticity. The high temperature tempering temperature is 500-600, the tempered structure is tempered Soxhlet plus spheroidal graphite, with toughness and strength well combined for 500-60d, and the tempered structure is tempered Soxhlet plus spheroidal graphite, which has good comprehensive properties of toughness and strength, so it is widely used in production.

Multi-temperature quenching of ductile iron: Ductile iron can obtain high strength after isothermal quenching, and has good plasticity and toughness. The selection of multi-temperature quenching heating temperature mainly considers to make the original tissue all A, without residual F, and also to avoid the growth of A grains.

The heating temperature is generally 30 50 above AFC1, and the isothermal treatment temperature is 0 350 to ensure that the lower bainite structure with comprehensive mechanical properties is obtained. After isothermal quenching of rare earth magnesium aluminum ductile iron b=1200 1400MPa, k=3 ,HRC 47 51. However, it should be noted that after isothermal quenching, a tempering process is added.

Surface quenching: In order to improve the surface hardness, wear resistance and fatigue strength of some castings, surface quenching can be used. Both grey and ductile iron castings can be case hardened. Generally, high (medium) frequency induction heating surface quenching and electrical contact surface quenching are used.

Chemical heat treatment: For castings that require surface wear resistance, oxidation resistance, and corrosion resistance, chemical heat treatment processes similar to steel can be adopted, such as gas soft chlorination, chlorination, boronization, sulfur seeping, etc.

HT300 has different heat treatment processes depending on the application environment and the required performance. Take the piston ring as an example: the quenching temperature is 880 900 meters, and the holding time is about 40 60 minutes; The tempering temperature is 500 600 and the tempering time is 90 120 minutes.

The heat setting temperature can be between 600 620 and the holding time is 45 to 80 minutes.

The quenching temperature is 880 degrees, keep for 80 minutes, quench with quenching oil (the specific composition is not clear) 70 degrees, and temper the temperature 240 degrees for 90 minutes.

There are many heat treatment processes for HT300, and the key is what kind of performance you want to get. It's a good choice.

Grey cast iron (HT200).

Standard: GB 9439-88 refers to gray cast iron with a minimum tensile strength of 200MPa.

Features and scope of application.

The tensile strength and plasticity are low, but the casting performance and shock absorption performance are good, and they are mainly used to cast pressure and vibration parts such as automobile engine cylinders, cylinder liners, and lathe beds.

Application examples: 1.The more important castings in general machinery manufacturing, such as:

Cylinders, gears, machine bases, metal cutting machine beds and bed surfaces, etc. 2Cylinder blocks, cylinder heads, pistons, brake wheels, coupling discs for automobiles, tractors, and piston rings for gasoline and diesel engines 3Inspection co-construction with a measurement plane, e.g

Scribing plates, V-shaped iron, flat rulers, level frames, etc. 4Hydraulic cylinders, pump bodies, valve bodies, and pump casings and containers that require a certain corrosion resistance of the code liquid to withstand the following medium pressures 5Circumferential speed》12 20m s pulleys and other parts that meet the listed conditions 6

Parts that need to be surface hardened.

This section is a cast iron grade.

High strength cast iron, the matrix is pearlite, the strength, wear resistance, heat resistance are good, and the vibration damping is also good; The casting performance is good, and manual aging treatment is required.

Working conditions in this paragraph.

1.Parts subjected to greater stress (bending stress< 2The pressure per unit area between the friction surfaces is greater than 10t, and the pressure of large castings working under wear is more than 10tIt is required to have a certain degree of airtightness or resistance to weak corrosive tarding media.

The strength requirements are not high, and the wear-resistant and shock-absorbing shape is complex, such as the cylinder block, cylinder head, reducer body, piston, brake wheel, coupling disc and diesel engine spine letter motor shell of the tractor.

Gray cast iron (HT200) is mainly used to cast pressure and vibration parts such as automobile engine cylinders, cylinder liners, lathe beds, etc.

1. Gray cast iron refers to cast iron with flake graphite, which is called gray cast iron because the fracture is dark gray when fractured. The main components are iron, carbon, silicon, manganese, sulfur and phosphorus, which is the most widely used cast iron, and its production chain accounts for more than 80% of the total output of cast iron.

2. According to the form of graphite, gray cast iron can be divided into: ordinary gray cast iron, and stone shed reed ink is flaked; ductile iron, graphite is spherical; Malleable cast iron, graphite in clump flocculent; Graphite cast iron, graphite is worm-like.