DE19528671C1 - Steel for linear construction profiles for underground pit mining - Google Patents

Abstract

The low-alloyed, high strength fine grain constructional steel contains 0.05-0.10% C, 0.05-1.5% Si, 1.5-2.3% Mn, 0.01-0.05% Al, 0.01-0.07% Nb, 0.01-0.04% Ti, 0.001-0.005% B, 0.0-0.4% Mo, 0.004-0.012% N and balance Fe, including up to 0.04% P and up to 0.02% S with bainitic structure, and is used as a material for the mfr. of hot-rolled linear construction profiles for underground pit mining, which must have the following mechanical properties in the hardened state; Re (yield point) > 700 N/mm<2>, Rm (tensile strength) > 800 N/mm<2>, A5 (extension) > 15% (DVM), and Av (impact work) (DVM)* > 60 J (at 20 deg C) (* = 10% cold deformed at 250 deg C/30'/L). Also claimed is a method for producing hot-rolled linear construction profiles esp. trough-shaped profiles for underground pit mining from the above steel comprising quenching the profile from the austenitic region to a temp. in the bainitic region at 5-50 K/s and then leaving to cool to room temp. in still air.

Description

The invention relates to the use of a low-alloy high-strength fine-grain structural steel for Line expansion profiles for mines and a Process for its manufacture.

According to DIN, a suitable steel for the pit expansion 21544 in tempered condition following guaranteed minimum Have strength properties:

Yield strength: R _e = 520 N / mm²
Tensile strength: R _m = 650 N / mm²
Elongation: A₅ = 18%
Notched impact energy: A _v (DVM) * ⁾ = 48 J (at + 20 ° C)

*) 10% cold worked + 250 ° C / 30 ′ / L (according to DIN 2544: artificially aged).

In DIN 21544, the steel grade 31 Mn 4 is 0.28 up to 0.36% C, 0.2 to 0.5% Si, 0.8 to 1.1% Mn, max. 0.045% P and S, min. 0.02% Al specified. That steel with the German material no. 1.0520 is used in the Delivery conditions hot-rolled, normalized or tempered offered. The remuneration treatment consists of one Quenching hardening temperature (in the austenite area) in Water or oil followed by tempering. The Hardening temperature is in the range of 850 to 920 ° C and the tempering temperature is at least 400 ° C.  

For the route expansion of mines u. a. Channel profiles (DIN 21544) used, the have different dimensions and meter weights to the to meet the static requirements placed on them. The profile TH 34 (34 kg weight) applies for example as a light profile, while TH 40 as a heavy profile referred to as. For handling the profiles under Days it is of great importance that the route expansion can be carried out with the lightest possible profiles. If now the expansion of a route due to existing mountain conditions, the profile TH 40 a steel with 520 N / mm² minimum yield strength, then the TH 34 profile could be used as well if the steel is accordingly higher Would have yield strength. The calculation of the static values of TH profiles result in such a Case that the yield strength must be about 700 N / mm².

There are also naturally hard steels for the pit expansion, see Stahl und Eisen, 104 (1984) No. 2, pp. 95-96 and DE 36 28 712 C2. This under the short name 17 Mn V 7 Steels that have become known contain 0.1 to 0.25% C, 0.25 to 0.6% Si, 1.0 to 1.8% Mn, 0.08 to 0.18% V, 0.2 up to 1.3% Cr and max. 0.06% Nb and 0.01 to 0.35% Ti, 0.25 to 0.55% Cu, balance iron. The steels have after a thermomechanical treatment and any subsequent normalizing ferritic-pearlitic Structure. In addition to ferrite and Perlite some bainite also occur locally. These well-known pit construction steels guide their mechanical Properties essentially from the high levels Carbon and manganese, the toughness through  finest precipitates of metal nitrides and Metal carbides is improved. With such steels the following properties are achieved:

R _e = 570 N / mm²
R _m = 724 N / mm²
A₅ = 22%
A _v (DVM) * ⁾ = 58 J (at + 20 ° C)

*) 10% cold worked + 250 ° C / 30 ′ / L.

This 17 Mn V 7 belongs to the naturally hard steels, whose Strength spectrum as I said through higher carbon and manganese levels are determined.

A channel profile for flexible route expansion of mines with an even higher carbon content in the range from 0.25 to 0.32% is known from DE 41 20 982 A1, which ensures a yield strength R _e <700 N / mm² in the tempered state. Steels with such a high carbon content achieve high strengths, but not sufficient toughness.

The invention is based on the object of a steel for section expansion profiles, in particular channel profiles, for mines to indicate the following Range of properties guaranteed:

R _e <700 N / mm²
R _m <800 N / mm²
A₅ <15%
A _v (DVM) * ⁾ <60 J (at + 20 ° C)

*) 10% cold worked + 250 ° C / 30 ′ / L

and also this range of properties can achieve simplified remuneration treatment.

This object is achieved according to the invention by Use a low alloy high strength Fine grain steel, consisting of

0.05 to 0.10% carbon
0.05 to 1.5% silicon
1.5 to 2.3% manganese
0.01 to 0.05% aluminum
0.01 to 0.07% niobium
0.01 to 0.04% titanium
0.001 to 0.005% boron
0.1 to 0.4% molybdenum
0.004 to 0.012% nitrogen

Balance iron and unavoidable impurities incl. Max. 0.04% phosphorus and max. 0.02% sulfur with bainitic structure as material for the production of hot-rolled section expansion profiles for mine operations, which in the tempered state the aforementioned Must have a range of properties.

In addition, the steel can contain up to 0.05% vanadium and Contain 1.2% chromium.

The inventive method for producing the Steel to be used according to the invention is thereby characterized that the profiles from the austenite area at 5 to 50 K / s to a temperature in the upper or quenched middle bainite area and then through the Residual heat under quasi-isothermal conversion to bainitic structure in still air at room temperature be allowed to cool.  

The coordination of the steel composition to this Heat treatment is essential to the invention.

The one consisting of hardness and self-tempering Remuneration treatment according to claim 3 is in itself from the DE 25 01 175 C3 known. It differs from conventional tempering, consisting of hardening through Quenching from hardening temperature to room temperature, and subsequent tempering to a temperature above 400 ° C in essentially in that the tempering treatment after Hardening is not carried out in a separate tempering furnace is, but takes place immediately after hardening. For this purpose, the curing process is controlled so that a certain residual heat remaining in the route expansion profile sufficient to temper the structure. For this the Hardening process in the bainite range (below 500 ° C) interrupted, d. H. the quenching treatment is at this temperature ended. Then in Section expansion profile still existing heat leads to Tempering the bainite formed, usually as Called self-starting. The further cooling process after Quenching of hardening temperature is completed in still air. This remuneration treatment has one Number of advantages. The shorter time should be emphasized for the entire remuneration treatment as well as the lower apparatus and energy expenditure.

Pit expansion profiles can be remunerated as follows:

For hardening, the profiles are, as usual, on a Austenitization temperature warmed, which is about 20 to 50 K above the Ac3 temperature of the steel used is around 900 ° C. The quenching is done with any cooling medium that the profiles with 5 to Cools 50 K / s. The quenching process is carried out during the Structural transformation into bainite, d. H. at a temperature of  500 ° C or lower, finished. After that, the profile remains left to itself with the residual heat. It takes place Transformation into bainitic structure followed by one Start yourself.

example

A TH 34 channel profile made of steel with the following Composition (% by weight) was made:

The steel was melted up in an oxygen converter cast in a continuous caster and in one Caliber rolling mill to profile TH 34 hot rolled. The hot-rolled profile was reheated after cooling and remunerated by hardening and self-tempering. Here the hardening temperature was 900 ° C. The deterrent has been when reaching a temperature in the core of the profile of 400 ° C ended, so that the structural change hardening structure formed by the residual heat of the profile was started. Examination of the profile revealed the following Mechanical property values:

R _e = 752 N / mm²
R _m = 907 N / mm²
A₅ = 17.0%
Z = 72.0%
A _v (DVM) * ⁾ 75 J, 93 J, 84 J (+ 20 ° C)

*) 10% cold worked + 250 ° C / 30 ′ / L.

For comparison, a TH 34 channel profile from the known steel 17 Mn V 7 in thermomechanically rolled Condition the required yield strength of more than 520 N / mm². This increases in the conventionally tempered state Yield strength to more than 700 N / mm². After a hardening and subsequent self-starting is only included 550 N / mm². It follows that not every steel comes with it is suitable, the required high mechanical Properties by interrupted hardening with subsequent self-starting in the residual heat to reach.

Claims (3)

1. Use of a low-alloy, high-strength fine-grain structural steel consisting of 0.05 to 0.10% carbon
0.05 to 1.5% silicon
1.5 to 2.3% manganese
0.01 to 0.05% aluminum
0.01 to 0.07% niobium
0.01 to 0.04% titanium
0.001 to 0.005% boron
0.1 to 0.4% molybdenum
0.004 to 0.012% nitrogen residual iron and unavoidable impurities including max. 0.04% phosphorus and max. 0.02% sulfur with a bainitic structure as a material for the production of hot-rolled section expansion profiles for mines, which must have the following mechanical properties in tempered condition: R _e <700 N / mm²
R _m <800 N / mm²
A₅ <15% (DVM)
A _v (DVM) * ⁾ <60 J (at + 20 ° C) *) 10% cold worked + 250 ° C / 30 ′ / L. 2. Use of a steel according to the composition Claim 1, which additionally up to 0.05% vanadium and up Contains 1.2% chromium for the purpose of claim 1. 3. Process for producing hot rolled Line expansion profiles, especially channel profiles, for Mine operations made of steel according to claim 1 or 2, characterized in that the Profiles from the austenite area with 5 to 50 K / s on one Temperature in the bainite area quenched and then through the residual heat during the further cooling Room temperature in still air.