2 The hardness gradient change before and after cryogenic treatment (1) was found to be significantly lower in the tooth surface from 0.05 to 0.15 mm, and the hardness at 0.05 mm from the surface was only 525 HV, which was converted to Rockwell hardness of 51 HRC, which is very obvious. The bowing phenomenon. After 0.2mm, the hardness increases and then gradually decreases to form a normal hardness gradient curve. The effective hardened layer depth is DC9.8550=1.42mm, so it is judged that the surface hardness is low.
(2) The above-mentioned tooth block is subjected to cryogenic treatment, that is, the hardness gradient is measured after deep cooling at -100 ° C for 4 hours, and the hardness of the curve 2 in the surface layer of 0.05 to 0.15 mm is increased to about 850 HV. Originally increased by more than 200HV. Therefore, the bowing phenomenon is eliminated, so that the gradient curve is normal, and the effective hardened layer depth is DC9.8550=1.45 mm, which is close to the original depth. This indicates that the original retained austenite in the surface layer continues to transform to martensite during the cryogenic treatment, thereby improving the hardness of the tooth surface and becoming unqualified as a good product.
(3) The above-mentioned cryogenically treated tooth block was further tempered at 180 ° C for 2 hours, and the change in hardness was observed. It is normal that its hardness is slightly reduced, but it is similar to the curve change after cryogenic treatment, without bowing. The effective hardened layer depth is DC9.8550=1.41mm.
3 Microstructural changes 4 Relationship between cold treatment temperature and hardness In order to clarify the effect of the temperature of the cold treatment on the hardness, the authors conducted experiments. Three tooth blocks were taken on the side of the carburized and quenched surface, and then ground and polished, and the surface of the sample was only polished by 0.05 mm, and then measured at three positions of the upper, middle and lower parts of the tooth piece sample. Hardness, and finally take the average of 3 points. The cold treatment temperatures were -40 ° C, -60 ° C, -80 ° C, -100 ° C, and the holding time was 4 h. As the cold treatment temperature decreases, the hardness gradually increases. It can be seen that the cold treatment at -40 ° C can promote the transformation of retained austenite to martensite, and increase the hardness. When the temperature drops to -60 ° C, the Vickers hardness can reach 800 HV or more. Therefore, the general low temperature box (-80 ° C) can be used for processing operations.
5 Discussion on the evaluation of retained austenite in metallographic standard (1) ZBT04100-88 automotive carburizing gear metallographic test professional standard is applicable to the evaluation of various carburizing steels such as 20Cr, 20CrMo and 20CrMnTi, in the production practice The evaluation of the needle length and carbide distribution of the body can be basically used in comparison, but the evaluation of retained austenite often causes contradictions.
(2) The first test indicator after gear carburizing and low temperature tempering is surface hardness. Therefore, in the case where the hardness of the tooth surface is acceptable, the thickness of the martensite should be mainly evaluated in the metallographic evaluation without emphasizing the pass or fail of the retained austenite. Because it is very inaccurate to evaluate the amount of retained austenite with a picture. If it is necessary to assess the amount of retained austenite, it is only reasonable to use other instruments to determine whether the residual austenite content in the surface layer is less than 30, but it is difficult to do in production.
(3) In production, tend to have low hardness in the outermost layer of the component. Generally, the hardness of the carburizing and quenching is more or less low, but it is considered that the lowest hardness of 表660HV in the surface layer of 0.05mm is suitable (660HV is converted into 58HRC). ). If there is obvious low hardness, and there is no decarburization, no tres and other structures on the surface, it can be rescued by a deep cryogenic treatment. Therefore, cryogenic treatment is an effective method to improve the quality of the workpiece.
(4) The steel parts published in the relevant literature can be deep-cooled within 1 h after quenching to effectively improve the hardness. This kind of statement is not necessarily suitable. For example, if 20CrMnTi steel is carburized and quenched for a long time and then cold treated, it can still obtain obvious effects.
Ratchet tie down
Nylon webbing belt ratchet tie down strap is used for tying down loads while transporting, shifting or moving them.
Ratchet Tie Down
Description
1. Color: Blue, yellow, orange or requirement
2. B.S: 800kg-10000KG
3. Strap Material: Polyester, nylon, Polypropylene, Poly-amide, PP, PE...
4. Width: 25MM - 100MM
5. Length: 25ft,27ft,30ft,6m,8m,8.2m,9m,10m,or customize length
6. Hook: with relative double j hook (or claw hook or flat hook) or customize
7. Certificate: TUV, GS, ISO 9001, according to EN12195-2
8. Remark: OEM orders are acceptable
9. Packing: Carton, Pallet for 800KG-10T plastic handle cargo ratchet strap.
10.Place of origin: Zhejiang, China (Mainland)
11.Production lead time: Within 25 days after order of 800KG-10T plastic handle cargo ratchet strap confirmed.
12.Notice: Polyester webbing is unaffected by water, oils, grease and most chemicals, although contact with strong alkali should be avoided.
Used for restraint of cargo on truck or trailer in transportation.
A wide variety of standard and heavy-duty fittings are available.
Caution: cargo lashings must NOT be used for lifting.
The main advantages of ratchet lashings are:
1. Custom logo or design.
2. Load restraint using a tensioning device (ratchet)
3. Effective and safe control of loads whilst transportation
4. Extremely quick and efficient tie down and release of load thus saving time.
5. No damage to the load being tied down.
Specifications:
|
size of Ratchet Tie Down |
25MM-100MM |
|
breaking strength of Ratchet Tie Down |
800KG-10000KG |
|
Length of Ratchet Tie Down |
4M to15M |
Products show
WARNING:
1.The slings should avoid the harm of the sharp instrument when lifting the goods.
2.Don't put something on the ratchet to avoid the danger.
3.Never use slings with damages or defects.
4.Forbidden to tie a knot of the sling or link with a knot. You should link the sling with the right connecting piece.
5.Only use slings with clear identifications.
6.Before use,check working load limit, length and working position.
7. Don't use the ratchet strap for lifting.
Ratchet Tie Down,Ratchet Belt Tie Down,Ratchet Tie Down Straps,Ratchet Straps
Hebei Liston Lifting Rigging Manufacturing Co., Ltd. , https://www.liftingriggingfactory.com