CN101787416B - Heat treatment normalizing process - Google Patents
Heat treatment normalizing process Download PDFInfo
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- CN101787416B CN101787416B CN 201010127384 CN201010127384A CN101787416B CN 101787416 B CN101787416 B CN 101787416B CN 201010127384 CN201010127384 CN 201010127384 CN 201010127384 A CN201010127384 A CN 201010127384A CN 101787416 B CN101787416 B CN 101787416B
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 18
- 238000000034 method Methods 0.000 title claims abstract description 14
- 239000000463 material Substances 0.000 claims abstract description 29
- 238000001816 cooling Methods 0.000 claims abstract description 23
- 238000005496 tempering Methods 0.000 claims abstract description 22
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 16
- 238000005516 engineering process Methods 0.000 claims description 9
- 235000019362 perlite Nutrition 0.000 claims description 8
- 239000010451 perlite Substances 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 238000000354 decomposition reaction Methods 0.000 claims description 2
- 238000012546 transfer Methods 0.000 claims description 2
- 229910000831 Steel Inorganic materials 0.000 abstract description 11
- 239000010959 steel Substances 0.000 abstract description 11
- 229910045601 alloy Inorganic materials 0.000 abstract description 3
- 239000000956 alloy Substances 0.000 abstract description 3
- 229910001562 pearlite Inorganic materials 0.000 abstract description 3
- 238000010079 rubber tapping Methods 0.000 abstract 1
- 229910001566 austenite Inorganic materials 0.000 description 8
- 229910000851 Alloy steel Inorganic materials 0.000 description 7
- 230000009466 transformation Effects 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 230000006698 induction Effects 0.000 description 4
- 238000012545 processing Methods 0.000 description 4
- 208000037656 Respiratory Sounds Diseases 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 230000002950 deficient Effects 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical compound OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 235000019628 coolness Nutrition 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
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- 230000000750 progressive effect Effects 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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Abstract
The invention discloses a heat treatment normalizing process suitable for small-size parts of 40 CrH steel and similar alloy constructional steel, which comprises the following steps of: step 1, enabling the rigidity of materials to be more than or equal to 26 HRC through normalizing, so that pearlite and upper bainite occur in material tissue, wherein the materials are heated to a first temperature which is at least above 50 DEG C more than the critical temperature Ac3 of the materials; step 2, decomposing the pearlite and the upper bainite in the normalizing tissue through tempering to adjust the rigidity of the materials to 20 to 26 HRC, wherein the tempering temperature is a second temperature; and step 3, cooling the materials through water-cooling after tempering and tapping. The heat treatment normalizing process can realize that the normalizing rigidity of the parts of the 40 CrH steel and the similar alloy constructional steel is controlled to be between 20 and 26 HRC, eliminate imbalanced tissue and realize the combination of the stable strength, toughness and mechanical properties of the materials.
Description
Technical field
The invention belongs to the metal heat treatmet category, relate in particular to the heat treatment normalizing process of a kind of 40CrH of being applicable to steel and the technical requirements of the high normalizing hardness of similar structural alloy steel small size part.
Background technology
40CrH steel and similar structural alloy steel are widely used in the manufacturing of parts such as gear, axle, transmission shaft, steering knuckle.Its machinery after surface heat is handled during as driving member is on active service, and the strength property of heart portion is had relatively high expectations.Certain company's turboshaft material is the 40CrH steel, and blank dimension is Φ 24 * 270 (mm), and material technology requires to be cold drawn back normalizing that normalizing hardness is 20～26HRC (Rockwell hardness).The Ac of 40CrH
3Critical temperature (ferritic transformation is austenitic finishing temperature during heating) is 788 ℃, if be heated to Ac by normal normalizing process
3The durometer level of forcing air cooling to obtain after+30～50 ℃ of insulations is 195～220HB (Brinell hardness), is converted into Rockwell hardness or actual Rockwell and measures, and its hardness does not meet the product design requirement all less than 20HRC.If adopt isothermal normalizing technology, in theory, as the C curve (supercooled austenite isothermal transformation kinetic curve, temperature-time curve) of Fig. 1, part is behind austenitizing, and cooling curve can be realized normalizing hardness 20～26HRC between passing through 680～550 ℃.But normalizing is in actual production, and the specific heat capacity of air is 1.3KJ/M
3℃, heat-conduction coefficient is 0.024W/M ℃, the about 4290KJ/M of the specific heat capacity of iron and steel
3℃, heat-conduction coefficient is 50W/M ℃, both gaps are huge, the 100Kg iron and steel are cooled to 650 ℃, 550 ℃ of about 60～80m of warm air of need from 900 ℃
3/ s flow velocity, obviously, this processing parameter is being difficult to control and realization under the technology status at present, and Equipment for Heating Processing manufacturers can not produce the practical isothermal normalizing equipment of producing at present.So the direct normalizing to 20 of 40CrH～26HRC hardness is required can't operate in the actual production.
Summary of the invention
The technical problem to be solved in the present invention is by the composite heat treating process to 40CrH and similar structural alloy steel small size part employing heat treatment normalizing, realizes the normalizing hardness requirement with normalizing Hardness Control to 20～26HRC scope.
The present invention is mainly by the following technical solutions:
A kind of heat treatment normalizing process, described technology comprises:
The first step makes material hardness more than or equal to 26HRC by normalizing, occurs perlite and upper bainite in the material structure; Wherein material is heated to first temperature, described first temperature is at least greater than the critical temperature Ac of material
3More than 50 ℃;
In second step, part perlite and upper bainite by in the tempering decomposition normalized structure transfer in 20～26HRC material hardness, and wherein tempering temperature is second temperature;
In the 3rd step, after coming out of the stove, tempering cools off by water-cooled.
Preferably, carry out forced air cooling in the described the first step normalizing.
Further, described forced air cooling is cooling fast, and material went out to cool off the rear surface temperature and was lower than 200 ℃ in 2 minutes cooling time.
Preferably, described first temperature range is 900～920 ℃.
Preferably, in described second step, the hardness according to the form below of second temperature after according to the first step normalizing chosen:
| Hardness after the normalizing (HRC) | Tempering range (℃) |
| 26～30 | 570～590 |
| 31～33 | 590～610 |
| ≥34 | 620～630 |
Further, be cooled to quick cooling in described the 3rd step, be 1 minute cooling time, and the material leaving water temperature(LWT) is 250 ℃.
The present invention is with the supercooled austenite isothermal transformation kinetic curve of 40CrH steel, temperature-time curve (see figure 1) and critical temperature Ac
3=788 ℃, Ar
1=665 ℃ is theoretical foundation, adopts 900～920 ℃ of heat tracings of comparatively high temps.Heating temperature improves, and alloying element to be dissolved in the austenite, and the austenite composition is even further, has increased the stability of supercooled austenite, and C curve is moved to right, and realizes that with suitable air-cooled speed supercooled austenite changes.When increasing forced air cooling speed, material hardness has reached 26～35HRC, and discreteness is big, and upper bainite occurred in the tissue.Upper bainite has tangible directivity, and hardness is higher.In machining process, because of itself and pearlitic nonhomogeneous hardness, form the difference of processed performance, thus very big in the discreteness of road, back processing geometric accuracy, cause gear rolling processing progressive error defective.Simultaneously, different with the perlite volume density because of upper bainite, transformation temperature is inconsistent during the induction quenching heating, and the swollen difference that rises of volume heat causes mid-frequency induction hardening crackle proneness to increase during phase transformation.
At durometer levels different after the normalizing (being different upper bainite content), formulate corresponding different destressing tempering temperature, decompose uneven phase upper bainite and high-density perlite, hardness is adjusted to 20～26HRC.Part adopted quick water-cooled after tempering was come out of the stove, and had avoided temper brittleness.
Description of drawings
Fig. 1 is the cooling characteristic C curve of 40CrH.
Embodiment
The present invention implements by following steps:
1. adopt the net belt type normalizing furnace at 900～920 ℃ scope internal heating, be incubated 60～80 minutes;
2. adopt three special blower fan forced air coolings on the cooling crawler belt, the air output of single blower fan is 4000～6000m
3/ h;
3. adjust cooling crawler belt walking speed, make material go out water cooling rear surface temperature and be lower than 200 ℃, be controlled at cooling time in 2 minutes;
4. with Rockwell hardness check normalizing hardness, according to the tempering process in the normalizing hardness selection step 5;
5. tempering temperature is selected from following table according to normalizing hardness, soaking time 60～90 minutes;
| Hardness after the normalizing (HRC) | Tempering range (℃) |
| 26～30 | 570～590 |
| 31～33 | 590～610 |
| ≥34 | 620～640 |
6. after tempering was come out of the stove, ℃ water outlet of the quick water-cooled to 250 of material was approximately 1 minute cooling time;
7. check hardness with Rockwell hardometer.
Normalizing involved in the present invention+destressing tempered recombining process is compared with general normalizing process, and normalizing temperature is increased to 910 ℃ from 860 ℃, and has increased the quick water-cooled road preface after tempering and the tempering.In the actual production if by normal normalizing process with 40CrH and the direct normalizing of similar structural alloy steel to hardness 20～26HRC be can't realize (once used continous way push-plate normalizing furnace, guipure normalizing furnace continuously, vacuum air-quenching furnace, little case chamber, laboratory stove were done repeatedly normalizing experiment, can't be with stable being controlled in 20～26HRC scope of normalizing hardness).
As everyone knows, heat treatment normalizing is defined as, with the Ac of METAL HEATING PROCESS to metallic substance
3In air, cool off after+30～50 ℃.Because the specific heat capacity of air and heat-conduction coefficient and iron and steel differ greatly.In actual production, can not require in time period and the temperature section temperature of part is as cold as 650 ℃ fast from 900 ℃ at C curve, and in 650～550 ℃ of temperature, keep the phase transformation fringe time, be the scope of 20～26HRC so can not get part normalizing hardness.Major cause is that 40CrH is the reasonable low alloy steel of a kind of hardening capacity, the surface cooling rate is fast, non-equilibrium microstructures such as upper bainite appear, upper bainite Soxhlet+body perlite mixed structure appears in the centre, the structural inhomogeneous discreteness that causes on the hardness is big, causes the defective and mid-frequency induction hardening crackle tendency of gear rolling.
Heat treatment normalizing process of the present invention has improved normalizing temperature, improved austenitic alloy unitization degree, increased the stability of supercooled austenite, postponed the transformation of supercooled austenite, obtained fine pearlite (sorbite)+ferrite+upper bainite phase blended normalized structure to perlite and upper bainite.Hardness is stabilized in 26～35HRC after the material normalizing.Through the technological test checking, according to the hardness after the normalizing tempering temperature has been made staging treating, hardness is carried out tempering by different tempering temperatures after the different normalizings.Through tempering, decomposed the uneven phase upper bainite in the tissue, the isometry ferrite can be adjusted to hardness in 20～26HRC scope, for the machining and the induction heat treatment in later stage provides favorable tissue and hardness, avoided the crackle that produces because of the unbalance microstructure rapid heating effectively; Improve the comprehensive mechanical performance of material.Water-cooled has then been restrained separating out of second phase fast, has prevented temper brittleness.
It is to be noted, the isothermal normalizing stove of present specialty, isothermal normalizing technology, even parameters such as the cooling rate before the isothermal, isothermal temperature, batch, heat exchange amount, cooling air quantity and medium temperature are accurately controlled, can not mass production 40CrH and similar structural alloy steel part normalizing hardness to 20～26HRC scope in.
Compare with present isothermal normalizing technology, advantage of the present invention is with 40CrH and similar structural alloy steel part, by above-mentioned technology, realizes normalizing Hardness Control to 20～26HRC scope, and can eliminate unbalance microstructure, realize intensity, the combination of toughness mechanical property of material settling out.
Claims (1)
1. heat treatment normalizing process, described technology comprises:
The first step makes material 40CrH hardness more than or equal to 26HRC by normalizing, occurs perlite and upper bainite in the material structure; Wherein material is heated to first temperature, described first temperature is at least greater than the critical temperature Ac of material 40CrH
3More than 50 ℃, first temperature range is 900～920 ℃; Wherein also need cool off fast in the normalizing of this step, material 40CrH went out to cool off the rear surface temperature and was lower than 200 ℃ in 2 minutes cooling time;
In second step, part perlite and upper bainite by in the tempering decomposition normalized structure transfer in 20～26HRC material hardness, and wherein tempering temperature is second temperature; The hardness of second temperature after according to the first step normalizing is chosen, and when durometer level after the normalizing was 26～30HRC, second temperature range was 570～590 ℃; When durometer level after the normalizing was 31～33HRC, second temperature range was 590～610 ℃; Hardness 〉=34HRC after normalizing, second temperature range is 620～630 ℃;
The 3rd step, after coming out of the stove, tempering cools off fast by water-cooled, and be 1 minute cooling time, and the material leaving water temperature(LWT) is 250 ℃.
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|---|---|---|---|
| CN 201010127384 CN101787416B (en) | 2010-03-18 | 2010-03-18 | Heat treatment normalizing process |
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|---|---|---|---|
| CN 201010127384 CN101787416B (en) | 2010-03-18 | 2010-03-18 | Heat treatment normalizing process |
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| CN101787416B true CN101787416B (en) | 2011-08-17 |
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| CN108796180B (en) * | 2018-07-06 | 2019-12-13 | 江苏南钢通恒特材科技有限公司 | 38B3 steel bar induction normalizing process |
| CN108796194A (en) * | 2018-07-06 | 2018-11-13 | 江苏南钢通恒特材科技有限公司 | 42CrMoA rod irons incude normalizing process |
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| US20060188384A1 (en) * | 2004-03-29 | 2006-08-24 | Kan Michael Y | High strength steel |
| CN100445400C (en) * | 2007-02-26 | 2008-12-24 | 济南二机床集团有限公司 | Heat treating method for improving mechanical property of 42CrMo |
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Owner name: SHANGHAI GKN HUAYU DRIVELINE SYSTEMS CO., LTD. Free format text: FORMER NAME: NATIEFU DRIVE SHAFTS CO., LTD., SHANGHAI |
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Address after: 201315 Cambridge Road 950, Cambridge industry zone, Shanghai, Pudong Patentee after: SHANGHAI GKN HUAYU DRIVELINE SYSTEMS Co.,Ltd. Address before: 201315 Cambridge Road 950, Cambridge industry zone, Shanghai, Pudong Patentee before: Shanghai GKN Drive Shaft Co.,Ltd. |
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