CN110681698A - 38MnS6L non-quenched and tempered steel rolling process - Google Patents

Abstract

The invention relates to a 38MnS6L non-quenched and tempered round steel rolling process which comprises the steps of heating by a heating furnace, removing phosphorus by high-pressure water, rough rolling, shearing, carrying out secondary phosphorus removal, fine rolling, hot sawing, sizing, segmenting, finishing and the like during medium rolling. The soaking temperature is reduced mainly in the soaking section of the heating furnace, so that the tapping rhythm is accelerated, the oxidation strength and the oxidation time of the steel billet in the heating furnace are reduced, and the iron oxide scale on the surface of the steel billet can be well removed in the high-pressure dephosphorization process; the secondary dephosphorization procedure is added in the middle rolling process, so that the iron oxide scale generated by surface reoxidation of the rolled blank in the conveying process is well eliminated, and the flux leakage initial detection qualified rate is improved to average 98.66% from about 40% in the prior art.

Description

38MnS6L non-quenched and tempered steel rolling process

Technical Field

The invention relates to 38MnS6L non-quenched and tempered round steel and a rolling process thereof.

Background

The automobile non-quenched and tempered steel is formed by combining a microalloying technology and a controlled rolling and cooling process, the quenching and tempering (quenching and high-temperature tempering) treatment process is omitted, the running energy consumption of an automobile accounts for 80%, the material production energy consumption accounts for 15%, and the automobile manufacturing energy consumption accounts for 5% through data display, 30 ~ 40% of the part manufacturing energy consumption can be saved by replacing the traditional quenched and tempered steel with non-modulated steel, the manufacturing cost can be reduced by more than 20%, the problems of deformation, cracking and the like caused by quenching in the quenching and tempering process can be reduced, the non-quenched and tempered steel can obtain higher strength without quenching and tempering after rolling, and the automobile non-quenched and tempered steel is green steel which can improve the production efficiency, reduce the production cost, is beneficial to energy conservation, emission reduction and environmental protection, and has wide application prospect.

38MnS6L non-quenched and tempered steel is one of the steel grades which are very challenging in the technical field of steel rolling and is applied to a crankshaft of an automobile engine, wherein the crankshaft is the most important part in the engine, and the crankshaft bears the force transmitted by a connecting rod, converts the force into torque, outputs the torque through the crankshaft and drives other accessories on the engine to work. The crankshaft is subjected to the combined action of centrifugal force of the rotating mass, gas inertia force of periodic variation and reciprocating inertia force, so that the crankshaft is subjected to the action of bending and twisting load. Therefore, sufficient strength and rigidity are required for the crankshaft, and the journal surface is required to be wear-resistant. Since 38MnS6L non heat treated steel is processed into a crankshaft by forging technology, the surface quality of this steel grade is extremely high, and the surface quality needs to be checked by a strict flux leakage flaw detection method. The existing rolling process comprises the following steps:

the first step is as follows: heating by a heating furnace, wherein the heating process heating standard is as follows: the temperature of the preheating section is less than 880 ℃, the preheating time is more than 45 minutes, the temperature of the first heating section is 850-1100 ℃, the temperature of the second heating section is 900-1200 ℃, the temperature of the soaking section is 1150-1200 ℃, the residence time of the high temperature section is 60-180 min, the total heating time is more than 150 minutes, and the steel tapping rhythm is 6 min/count;

the second step is that: removing phosphorus by using high-pressure water, and removing iron oxide scales on the surface of the steel billet by using the high-pressure water;

the third step: roughing in a two high reversing mill (phi 1100 x 2500);

the fourth step: 1# hydraulic shearing head, cutting off defects at the end of the rolled blank;

the fifth step: and (4) carrying out medium rolling by 6 continuous rolling mills, wherein all the medium rolling mill sets are horizontally and vertically arranged alternately and are fifth-generation short-stress rolling mills. The composition of the rolling mill is phi 750x 6;

and a sixth step: and 4, finish rolling is carried out by a continuous rolling mill, and all finishing mill groups are horizontally and vertically arranged alternately and are short-stress rolling mills of the fifth generation. The composition of the rolling mill is phi 550x4, and the rolling is controlled in a torsion-free, micro-tension or tension-free manner in the whole line;

the seventh step: hot sawing, sizing and segmenting, namely segmenting by using a grinding wheel saw after sizing by using a sizing machine;

eighth step: and (4) finishing, namely receiving round steel for chamfering and straightening.

In the prior art, in the heating process of a heating furnace, the enrichment of Si element occurs on the interface of the iron oxide scale on the surface of a billet and a steel matrix, after high-temperature oxidation, a composite oxide of Si and Fe is formed and embedded into the steel matrix, the adhesion is strong, so that the descaling is not clean, the rough rolled billet is conveyed to the next procedure for intermediate rolling, the rolled billet is oxidized again in the conveying process, the surface generates more iron oxide scales, the iron oxide scales are pressed into the matrix along with the metal flow in the subsequent rolling process, so that the surface of the finished round steel has pitted surface and continuous crack defects, the magnetic leakage initial detection qualification rate of the product round steel is only about 40%, the production cost of the product is greatly increased, the order delivery is influenced, and the market competitiveness of a company is reduced.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a rolling process of 38MnS6L non-quenched and tempered steel, which effectively solves the problem of low magnetic leakage initial detection qualification rate of 38MnS6L non-quenched and tempered steel, thereby greatly reducing the production cost, improving the production efficiency and ensuring the delivery of orders.

In order to achieve the purpose, the technical scheme provided by the invention is as follows: a rolling process of 38MnS6L non-quenched and tempered steel comprises the following steps:

the first step is as follows: heating by a heating furnace, wherein the heating process heating standard is as follows: the temperature of the preheating section is less than 880 ℃, the preheating time is more than 45 minutes, the temperature of the first heating section is 850-1100 ℃, the temperature of the second heating section is 900-1200 ℃, the temperature of the soaking section is 1100-1150 ℃, the residence time of the high temperature section is 60-180 min, the total heating time is more than 150 minutes, and the steel tapping rhythm is 4.5 min/count;

the second step is that: removing phosphorus by using high-pressure water, and removing iron oxide scales on the surface of the steel billet by using the high-pressure water;

the third step: rough rolling, rough rolling with a two high reversing mill (phi 1100 x 2500);

the fourth step: shearing, and cutting off the end defects of the rolled blank;

the fifth step: middle rolling, wherein all the 6 continuous rolling mills are arranged horizontally and vertically in an alternating mode, the rolling mills are phi 750x6, and the rolling mills are fifth generation short stress rolling mills; a dephosphorization device is arranged at the outlet of the 2V rolling mill, and the steel billet is subjected to secondary dephosphorization in the middle rolling process;

and a sixth step: finish rolling, wherein the rolling mill has the composition of phi 550x4, is a fifth generation short stress rolling mill, is arranged horizontally and vertically in an alternating mode, and realizes torsion-free, micro-tension or tension-free controlled rolling on the whole line;

the seventh step: hot sawing, sizing and segmenting, namely segmenting by using a grinding wheel saw after sizing by using a sizing machine;

eighth step: and (4) finishing the received round steel to perform chamfering and straightening.

The invention has the beneficial effects that: the heating temperature is reduced by the heating process of the heating furnace, the steel tapping rhythm is adjusted from 6 min/branch to 4.5 min/branch, the oxidation time of the steel billet in the heating furnace is reduced, and the iron oxide scale on the surface of the steel billet can be well removed in the high-pressure dephosphorization procedure; the secondary dephosphorization procedure is added in the middle rolling process, so that the iron oxide scale generated by surface reoxidation of the rolled blank in the conveying process is well eliminated, and the flux leakage initial detection qualified rate is improved to average 98.66% from about 40% in the prior art. Although the secondary dephosphorization procedure is added, the production cost is increased, the dephosphorization device is simple, equipment does not need to be changed, the additional installation cost is low, the secondary iron scale formed on the surface of the round steel is effectively removed, the problems of pitted surface and continuous crack defects on the surface of 38MnS6L non-quenched and tempered round steel are solved, the initial detection qualified rate of the magnetic leakage of the round steel is greatly improved, the production efficiency is greatly improved, the production cost is greatly reduced, and the product competitiveness is improved.

Detailed Description

The technical solution of the present invention is described in detail below with reference to examples.

The embodiment of the invention takes 5 rolling batches of 38MnS6L non-quenched and tempered round steel 38MnS6L-852F with the same specification as an example, and compares the example with 5 rolling batches of 38MnS6L-852F non-quenched and tempered round steel with the same specification produced by the prior art to illustrate the beneficial effects of the invention.

Selecting 10 production orders of 38MnS6L non-quenched and tempered round steel with the same specification, and checking the surface state of a continuous casting billet on site to ensure that the surface of the billet meets the appearance quality requirement; the 10 rolling batch order 38MnS6L non-tempered steel billets were divided into two groups, group 1: 5 rolling batch numbers of 7C91245, 7C91246, 7C91247, 7C91248 and 7C 91249; group 2: 8C24964, 8C24965, 8C24966, 8C24967, 8C24968 total 5 rolling batches.

Table 1: heating process control meter

The comparative example is produced according to the tapping rhythm of 6 min/count, and the embodiment of the invention is produced according to the tapping rhythm of 4.5 min/count.

The phosphorus removal device is started at the 2V outlet of the medium rolling mill in the embodiment of the invention to carry out secondary phosphorus removal.

Two groups of finished products 38MnS6L are counted, wherein the magnetic flux leakage initial probing qualification rate of the non-quenched and tempered round steel is as follows:

38MnS6L non-quenched and tempered steel is produced by the existing rolling process to jointly produce 457 fixed sizes, and the flux leakage initial detection qualified rate is 42.70%; the rolling process of the invention is adopted to roll and produce 463 fixed lengths together, and the flux leakage initial detection qualified rate is 98.66%. Practice proves that the production efficiency is greatly improved, the implementation is convenient and simple, unexpected technical effects are achieved, and the method has high popularization value.

Claims (1)

1. A rolling process of 38MnS6L non-quenched and tempered steel comprises the following steps:

the first step is as follows: heating by a heating furnace, wherein the heating process heating standard is as follows: the temperature of the preheating section is less than 880 ℃, the preheating time is more than 45 minutes, the temperature of the first heating section is 850-1100 ℃, the temperature of the second heating section is 900-1200 ℃, the temperature of the soaking section is 1100-1150 ℃, the residence time of the high temperature section is 60-180 min, the total heating time is more than 150 minutes, and the steel tapping rhythm is 4.5 min/count;

the second step is that: removing phosphorus by using high-pressure water, and removing iron oxide scales on the surface of the steel billet by using the high-pressure water;

the third step: rough rolling, rough rolling with a two high reversing mill (phi 1100 x 2500);

the fourth step: shearing, and cutting off the end defects of the rolled blank;

the fifth step: middle rolling, wherein all the 6 continuous rolling mills are arranged horizontally and vertically in an alternating mode, the rolling mills are phi 750x6, and the rolling mills are fifth generation short stress rolling mills; a dephosphorization device is arranged at the outlet of the 2V rolling mill, and the steel billet is subjected to secondary dephosphorization in the middle rolling process;

and a sixth step: finish rolling, wherein the rolling mill has the composition of phi 550x4, is a fifth generation short stress rolling mill, is arranged horizontally and vertically in an alternating mode, and realizes torsion-free, micro-tension or tension-free controlled rolling on the whole line;

the seventh step: hot sawing, sizing and segmenting, namely segmenting by using a grinding wheel saw after sizing by using a sizing machine;

eighth step: and (4) finishing, namely receiving round steel for chamfering and straightening.